This invention relates to a method for producing a cigarette filter rod. More particularly, this invention relates to a method for applying an additive to a filter rod during its manufacture in the form of a liquid additive foam.
Cigarette filter rods are commonly made from a filamentary material. One commonly used filamentary material is cellulose acetate. More recently, filamentary polyolefin materials, particulary fibrillated polypropylene, have emerged as possible filter materials. Other filamentary materials that could be used are wood pulp fibers, cotton, flax, jute, wool, silk, ramie, protein fibers, polyamide fibers (e.g., nylon) cellulose, regenerated cellulose (e.g., rayon), other cellulose ester fibers (e.g., cellulose triacetate), acrylic fibers, polyester fibers, and polyvinyl chloride fibers. Filter rods can also be made from gathered paper.
In the case of a filamentary material, typically provided in bale form, the material is drawn into a bundle or "tow"of ten to thirty thousand filaments. The tow is then spread and fluffed up, or "bloomed", usually by being placed under tension and passed over air jets. The bloomed tow is passed through a funnel or other constricting device and then through a shaped aperture to form the filter rod. The rod is provided with an outer layer to maintain its shape, either by being wrapped with a plug wrapping of paper or other sheet material, or being heated to fuse the outermost filaments into a self-supporting layer.
A filter rod produced as described above may not be firm enough to be self-supporting or, while self-supporting, may not give a firm enough subjective feel to smokers. Therefore, plasticizers or binders are usually added to the tow during or after blooming. These additives cause the filaments to bond to each other at their cross-over points when the tow is gathered, giving the rod an increased firmness. A filter rod so treated must be cured either by heating for a short time or by air-curing.
In some cases, it is desirable to apply other additives to a cigarette filter rod such as flavorings (which form an aerosol when contacted by the hot tobacco smoke and flow with the smoke into the smoker's mouth) or humectants.
It is known to apply these additives to the tow by spraying them in liquid, mist, or aerosol form onto the tow during or after blooming. With spray application methods, overspray of the additives is common. Overspray, the amount of additive which does not directly impact on the tow, causes several problems. First, controlled uniform application of additive to the tow is difficult to achieve. While accurate metering systems may be employed to measure the amount of additive sprayed, it is difficult to determine in real time what percent of additive sprayed actually is retained by the tow. Second, if the composition of the additive includes low vapor pressure solvents, spray techniques generate high concentrations of the solvent in the environment. Third, overspray of additives which are viscous or sticky tends to cause machine part contamination and the overspray cannot be collected for re-use.
In addition, it is sometimes desirable to apply an additive in small concentrations, i.e., less than about 10% of the dry filter weight. This necessitates the use of solvents to deliver a small amount of additive over the large surface area of the filaments in the tow. These solvents must then be removed by drying or by allowing them to evaporate. The solvents may also stain the plug wrapper or the overlying tipping paper. Further because of the lack of control, some of the additive is wasted. Finally, viscous additives such as binders and adhesives may contaminate machine parts in the plug making apparatus, requiring frequent cleaning, because excess additive must be used to get the proper amounts added to the tow.
It would be desirable to be able to apply additives uniformly to a cigarette filter rod without overwetting the fibrous web of the filter tow, and without contaminating machine part in the plug making apparatus.